The present invention relates to a digital television comprising a digital television combination integrated circuit, including a video signal D/A converter which converts a digital video signal into an analog video signal.
Along with the spreading of digital television systems in recent years, the integration of the circuitry which makes up digital television receivers has steadily progressed.
In the past, the circuitry in a digital television was built using separate integrated circuits adapted for various types of signal processing, but recently it has been possible to perform these various types of signal processing with a single integrated circuit. For example, a digital television combination integrated circuit is in use, which processes both a digital video signal and a digital audio signal.
On the other hand, a device which performs signal processing upon the video signal and the audio signal while associating them together organically is disclosed in Japanese Laid-Open Patent Publication H08-289224. The audio amplification circuit disclosed in this publication is one with which an audio output is obtained which is suited to the human visual and auditory senses, by controlling the level of amplification and the frequency characteristics of the audio signal based upon the video information.
Although, by employing the above described digital television combination integrated circuit, the total number of components in the digital television is reduced, and it can be built more compactly, thus reducing its cost, nevertheless, since this type of combination integrated circuit is one which is used by a plurality of manufacturers, therefore a large number of functions for enhancing its general utility as a component are included in advance. However, when building a circuit according to the requested specification for a digital television, sometimes functions which are necessary for this specification are not included, and naturally, in such a case, it has been necessary to build up the circuit by using other integrated circuits in parallel.
For example, when building a circuit in which, in order to adjust the sound volume, the audio signal is converted into an analog audio signal by being PWM modulated and then passed through a low pass filter, then it is necessary to provide the PWM modulation circuit and the low pass filter or the like as separate dedicated components, and this constitutes an obstruction to reduction of the cost. Moreover, with a circuit in which the control of the sound volume is performed by the above described PWM duty ratio, generally the stability of the temperature characteristic is low, and it is difficult to adjust the sound volume with high accuracy. Furthermore, although it is possible to provide a ladder resistor externally, and to employ a circuit which performs adjustment of the sound volume by changing the voltage division ratio provided by this resistance, with this simple circuit it is only possible to change the sound volume stepwise, so that there has been the problem that it has not been possible to adjust the sound volume substantially continuously.
Due to this, it is often impossible to utilize some among the large number of functions which are provided in advance within such a combination integrated circuit in an effective manner, and moreover it sometimes becomes necessary to provide separate components externally in order to build up the circuitry which is required; and this state of affairs is a problem which must be solved if it is contemplated to make a digital television more compact and to reduce its cost.
It should be understood that, with the audio amplification circuit disclosed in the above Japanese Laid-Open Patent Publication H08-289224, only processing while organically associating the video signal and the audio signal is contemplated, and making the system as a whole more compact and reducing its cost are not taken into account, so that this prior art is not one which can solve the problems described above.
The object of the present invention is to provide a digital television with which a reduction in the number of component parts may be anticipated, whereby, along with reducing the size of the substrate, it is also possible to make the overall structure lighter and more compact, thus reducing the cost.